Polyhydramnios
Prevalence and causes
The prevalence of olyhydramnios ranges from 1% to 2%.1,25 Table 5 displays the most commonly used cutoffs for AFV in relation to severity of polyhydramnios.1,25
Idiopathic polyhydramnios is most commonly mild (55%). Causes of polyhydramnios include uncontrolled maternal diabetes; large-for-gestational-age fetus or birth weight >90th percentile; movement disorders (neuromuscular disorders) that affect fetal amniotic fluid swallowing; and multiple gestations (most commonly in the context of twin-twin transfusion syndrome, associated with oligohydramnios in the co-twin).Certain fetal anomalies (associated or not with genetic conditions) are more often associated with severe polyhydramnios; the combination of FGR and polyhydramnios is suggestive of chromosomal aneuploidy (ie, Trisomy 18 or 13).26 Table 6 displays the fetal anomalies described in association with polyhydramnios. Visualization of fetal anatomy can be hampered by the excessive amniotic fluid volume (the fetus may be positioned far from the U/S transducer or fetal movements may be excessive). Placing the mother in lateral decubitus or performing an amnioreduction may facilitate U/S visualization (Table 6).
Rare conditions associated with polyhydramnios include fetal anemia and/or heart failure (eg, polyhydramnios with hydrops), placental tumors (eg, chorioangiomas), and congenital infections. After birth, an abnormality is diagnosed in up to 25% of cases that prenatally had been considered idiopathic.29